Electric incandescent lamp



July 28, 1936. c. TROPE 2,049,338

ELECTRIC INCANDESCENT LAMP Filed March 12, 1935 Ihvehtor Car! Trope 6AM by i -lmttorney Patented July 28, 1936 PATENT OFFICE ELECTRIC INCANDESCENT LAMP Carl Trope, Berlin-Steglitz, Germany, assignor to General Electric Company, a corporation of New York Application March 12, 1935, Serial No. 10,723 In Germany April 10, 1934 2 Claims.

My invention relates to electric incandescent lamps and particularly to multiple filament lamps. Still more particularly my invention relates to incandescent lamps comprising two or more filaments, one of which is normally operative, and means for automatically bringing into the electrical circuit another filament when the normally operative filament burns out.

In lamps of the type referred to above it has heretofore been proposed to provide a spring switch which isheld in the open position by the normally operative filament and released by the burning out of said filament, thereby closing the circuit through another filament. Such devices have not come into practical use because the tensile strength of the filament when heated to an incandescable temperature is too low to provide a positive means for holding the spring switch in the open position. In another proposed arrangement, the normally operative filament was divided into two branches connected in parallel and the mid points of said branches were connected by wires to the ends of a fuse wire which was bent around the end of a spring switch arm. When one of the branches of the normally operative filament burned out, the balance of current In the branches was upset so that some current passed through the fuse and ruptured it, there- 30 by releasing the said switch arm and connecting a second filament in the circuit. This structure was objectionable because it was so'complicated and the fuse, being stressed intensively at one point in a lateral direction .by the spring switch arm, was liable to be broken prematurely, particularly if subjected to vibrations.

The present invention is based on the fact that when a filament burns out, the current rises as the windings of a coiled filament come in contact or as a small arc is formed between the.

broken parts of the' filament. This is particu uarly so when the lamp has a gas filling rich in argon and the filament is of a concentrated form such as a coiled coil. This rise in cur-- 45 rent is suflicient to rupture a wire-shaped fuse connected in series with the filament. With this knowledge as a basis a considerably simplified construction of multiple filament lamp may be made by connecting a spring switch arm in series 50 with a fusewire which is also in series with the normallyoperatlve filament. When the filament bums out and the current rises, the fuse -is rup-.

tured and the switch arm is released, thereby connecting another filament in the circuit. i For a further understanding of the invention,

reference may be had to the drawing in which Fig. 1 is a diagrammatic view of the circuit arrangement of a lamp comprising my invention; and Fig. 2 is a similar view of a slightly modified circuit.

Referring to Fig. l, the lamp comprises a normally operative filament I0 and an auxiliary filament I I which are sealed in the usual glass bulb (not shown). The said filaments are connected at one side to a common lead wire I3 which is 10 electrically connected to one of the lamp'base terminals. The opposite ends of said filaments Ill and II are connected to lead wires- I4 and I5 respectively, said lead wire I4 being electrically connected to the other lamp base terminal. A fuse wire I6 and a spring switch arm I! are incorporated in the lead wire I4 in series with the filament Ill. The switch arm I! may be provided with a contact I8 and the lead wire I5 with a contact I9. Since the switch arm IT, or its contact I 8, is held out of engagement with the lead wire I5, or its contact I9, by the fuse wire I6, only the filament I 0 is normally operable. When the said filament I0 burns out, the fuse I6 25 is ruptured by the rising current flow, thereby releasing the spring switch arm I'I so that the contact I8 thereon engages the contact I9 and connects the auxiliary filament II into the circuit. The rupturing of the fuse I6 also prevents the 30 blowing of the main fuse located in the supply line.

In Fig. -2 parts corresponding to similar parts in Fig. 1 have been correspondingly numbered. The lead wire I3 is connected directly to filament II] as in Fig. l, but a separate branch lead wire 20 is connected to said lead wire I3 and to the filament I I, and a fuse wire 2| is incorporated in said lead 20 to prevent blowing of the main line fuse when the auxiliary filament II burns out.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In an electric incandescent lamp, the combination of a normally-operative filament and an auxiliary filament, one end of each of said filaments being electrically connected to one ter-- minal of the lamp, a spring switch arm electri- 'cally connected at one end to the other terminal of the lamp, and a fuse wire in series with said normally operative filament. connected to the other end of said switch arm and holding said switch arm out of circuit engagement with said auxiliary filament, said fuse wire being of sufficient size to carry the normal current through said normally operative filament but not an ab- 1 normal current, said switch arm moving into cirwire, and a fuse wire in series with said normally operative filament connected to the other end of said switch arm and holding said switch arm out of engagement with said lead wire of said auxiliary filament, said fuse wire being of sufficlent size to carry the normal current through said normally operative filament but not an abnormal current, said switch am moving into engagement with the said lead wire of said auxiliary filament to close the circuit therethrough when re- 10 leased by the rupturing of said fuse wire.

CARL more. 

